The specific objective of the studies proposed herein are designed to determine the manner in which the arterial wall responds to a sustained increase in arterial blood pressure. Hypertension will be produced by two methods: a) desoxycorticosterone acetate plus saline, and b) unilateral renal artery stenosis. Studies will be performed on segments of carotid, femoral and tail arteries including active and passive (smooth muscle) mechanical properties, and compositional analyses. Transmural pressure and external diameter measurements will be made on intact, cylindrical segments of arteries in vitro under conditions of active (norepinephrine) and passive (2 mM-EGTA) smooth muscle. These data will be used to determine pressure-diameter and stress-strain relations as well as values of incremental moduli and characteristic impedance with emphasis on the effects of smooth muscle activation. Active smooth muscle responses will be quantitated in terms of wall stress development as a function of artery diameter and constriction responses as a function of transmural pressure. Analysis of composition will include a) connective tissue content (collagen and elastin), b) contractile protein content (myosin and actin), and c) water and electrolyte content (Ca ion 2, Mg ion 2, K ion, Na ion and Cl-). A comparison of mechanics and composition will be made between normal and hypertensive arteries to determine a) the time course of changes in arterial wall properties with the duration of hypertension, b) the effects of initial animal age on arterial wall responses to hypertension, and c) the reversibility of these arterial wall changes with normalization of blood pressure. These studies will be performed using Wistar rats.